where \(\bf u\)  is the flow velocity, and \(\psi = C^{3} - 1.5 C^{2}+ 0.5 C -\mbox{\textit {Cn}}^{2} \nabla ^2 C\)  the chemical potential. We set the Péclet number \(\mbox{\textit {Pe}}=0.9/\mbox{\textit {Cn}}\)  and the Cahn number \(\mbox{\textit {Cn}}=0.75\Delta x/H\)  with \(\Delta x\)  being the mesh size and \(H\)  being the height of the RB cell. The parameters \(\mbox{\textit {Pe}}\)  and \(\mbox{\textit {Cn}}\)  are taken according to the sharp-interface approach proposed in [1]}, [2]}, [3]}.
